Robot: ProtoBot

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ProtoBot Foundations...

This robot has odd origins... I needed a test platform for the high power H-Bridge design I have come up with for the Neighborhood Roving Platform (NeRP) project. Given that the NeRP project has 10 of these integrated into a single design I thought it best to design and build a single functional module with which to test. Given that I have some motor / gearbox combinations here in the studio for use in a different project, a coworker of mine suggested that I produce a pair of the new amplifier boards, clamp the whole mess to a piece of plywood and test drive it around the studio floor.

Of course there are a number of other functions I need to integration test and if I am going to develop the PID functionality on this platform, then I'll need to integrate the IMU and several other functions. At this point the reader may be thinking feature creep, and that is exactly what this project is... It is a fun string of feature creep that turned a high powered motor driver board into a fully developed robot.

There is a lot more to share about tasks and foundations, and since this project shares a common lineage with the NeRP project (below) I encourage the reader to follow on on section 00 of that project.

Timeline...

The primary build of the ProtoBot project was started and completed in a single year, 2007. The electrical design of the five primary CCAs stated in December '06 over the Christmas Holiday. The mechanical fabrication started shortly there after in January and was continued on into late spring / early summer. Work was interupted for approx~2 months with my employer flying me around to the country to work with various customers and witness subcontractors product qualification testing. Yeah, sigh there is nothing worse being stuck in a hotel in the rainy months in Oregon when all of your hobbies are 1600 miles away, sigh... Upon returning, a few last small parts were finished-up and software integration and debugging began in Ernest. ProtoBot made its first public debut in Dallas, in Nov. of 2007. Subsequent software development and testing is an on-going task and will likely last a few additional years...

Overview / Objectives:

ProtoBot exists as a simple 4 wheeled robot with differential steering and no suspension components. Differential steering is implemented through the use of #35 stainless steel chain connecting the gearbox output to both wheels at the same time. As the structural plates are designed to be extremely simple to make they could just have easily have been cut from wood on a table saw. The only reason for the extensive lightening holes and extra material removal is to lighten the overall chassis.

The mast is a derivation of several previous designs and observations of armature roboticists who's work proceeded me. Their observations show magnetic effects of the fields of motors and other radiated EMI fields on stationary fields like the earth's magnetic field thus influencing the readings of magnetic compassrd and IMU's like the one by micro-strain that I will be using. Rather than spend a large amount of time shielding all of the various components it is much easier to merely separate the components with physical space. Additionally, the adjunct of the mast allows for the separation of the antenna of the two independent radio systems to keep their internal heterodynes from interfering with each other.

The primary objectives for ProtoBot as a stepping stone prototype in the design, build and test of NeRP are four fold:

Characterize the motors and their expected performance as these same motors will be used in the propulstion systems for NeRP.

Design, Fabricate and Test motor amplifier / drivers that can handle the high currents and required closed loop feedback.

Develop a good protion of software base that can be refactored into the NeRP development.

Integrate, test and characterize a number of sensors including:

Sonar distance ranging

Infra-Red distance ranging

Global Positioning System

Inertial Managment Unit

Requirements:

Even a simple test platform needs requirements. One of the biggest tricks to writing good requirements is to clearly state what we are going to build with-out stating how one is to go about building it. (what vs how) It is worth noting that in addtion, requirements specify the performance against which the verification, validation and testing (VV&T)can be measured. Finally, a good requirements capture allows one to define all the interfaces between the various subsystems and prior to detailed design work, asure compatability.

Max's Little Robot Shop is a one man operation with an end goal of having fun playing with robotics. As such the requirements captured here-in are necessarily 'light'. The goal here is to make sure the essence of the development task is captured and documented sufficnetly that the end project adequatly meets the need of the original request.

Environmental:

All vehicle functions shall have full performance across specified environmental ranges.

Vehicle data telemetry system shall incorporate periodic "is-alive" or "heartbeat" function even while radio comms are in low power shutdown waking up for only minimal transmission, while maximizing power conservation.

Vehicle design shall through the use of shielding, geometric constraints or seperation, prevent interferance between the multiple radio systems, sensors and propulsion elements known to cause destructive interference.

Nice to have:

Vehicle should provision excess power to carry its own support equipment & tools given a substantial sacrafice in performance metrics.

Vehicle should provision excess power to carry its operators support equipment & supplies given a substantial sacrafice in performance metrics.

Vehicle should operate quietly, not raising ambient SPL above 20dB(NTE) when measured at 36-in. (Note: This approximates rustling leaves in a breeze, or a calm room)

Expansion:

Future planned enhancments to the basic ProtoBot platform will included additional layered sensor suites, an arm for payload retrieval / delivery, a ping pong ball gun and a APU. Where possible provisions should be made to facilitate the staged design and integration of these applications. Consideration should be given to processing power and memory, power switching / interconnects and mechanical mounting points.

References:

For those following the development of the robots on this site, the following outlines a short list of must visit related web sites.